This invention relates to method of forming a refractory metal (preferably, tantalum) oxide layer, and particularly to a method of forming a tantalum pentoxide layer, on a substrate using a reactive deposition process with a refractory metal precursor compound with an ether.
In integrated circuit manufacturing, microelectronic devices such as capacitors are the basic energy storage devices in random access memory devices, such as dynamic random access memory (DRAM) devices, static random access memory (SRAM) devices, and ferroelectric memory (FERAM) devices. Capacitors typically consist of two conductors, such as parallel metal or polysilicon plates, which act as the electrodes (i.e., the storage node electrode and the cell plate capacitor electrode), insulated from each other by a layer of dielectric material.
The continuous shrinkage of microelectronic devices over the years has led to a situation where the materials traditionally used in integrated circuit technology are approaching their performance limits. Silicon (i.e., doped polysilicon) has generally been the substrate of choice, and silicon dioxide (SiO2) has frequently been used as the dielectric material to construct microelectronic devices. However, when the SiO2 layer is thinned to about 10 xc3x85 (i.e., a thickness of only 4 or 5 molecules), as is desired in the newest micro devices, the dielectric layer no longer effectively performs effectively as an insulator due to the tunneling current running through it. This SiO2 thin layer deficiency has lead to a search for improved dielectric materials.
Refractory metal oxides such as tantalum pentoxide (Ta2O5), titanium dioxide (TiO2), zirconium dioxide (ZrO2), and hafnium dioxide (HfO2), are some of the most promising SiO2 replacements for future DRAM devices since they meet the requirements for large scale processing and fabrication using conventional microelectronics processing equipment. Furthermore, these oxides have excellent step coverage, and they exhibit comparatively low leakage current. Ta2O5 is of particular interest as layers of amorphous Ta2O5 have a dielectric constant of about 25. Ta2O5 layers can be formed using chemical vapor deposition (CVD) processes. For example, reacting vapors of Ta(OC2H5)5(pentaethoxy-tantalum) with oxygen or by reacting vapors of TaF5 with an O2/H2 plasma can form Ta2O5.
Annealing can improve the crystallinity and resulting dielectric constant of refractory metal oxide layers. For example, the dielectric constant of an amorphous Ta2O5 layer can be increased to at least 40 by annealing the deposited layer at temperatures over 700xc2x0 C., causing a change in crystallinity from an amorphous state to what is believed to be a preferred (001) orientation of a crystalline hexagonal phase of Ta2O5. Unfortunately, this increase in dielectric constant of annealed crystalline Ta2O5 layers is counterbalanced by higher leakage currents through the crystal boundaries. High temperature annealing of a Ta2O5 layer on polysilicon also inevitably produces a thin SiO2 interfacial layer between the Ta2O5 layer and the polysilicon due to ambient oxidation during the deposition process and during any post-processing such as annealing. This SiO2 layer insures better interfacial properties but also causes a reduction of the global dielectric constant of the Ta2O5 capacitor. A metal nitride barrier layer can be applied to the polysilicon substrate prior to formation of the Ta2O5 layer to avoid formation of the SiO2 interfacial layer but at the cost of adding another processing step. Metal nitride barrier layers are also likely to be oxidized by high temperature anneal processes.
Changing the nature of the substrate and curing conditions during CVD processing can improve the dielectric constant of resulting Ta2O5 layers. For example, Kishiro et al., xe2x80x9cStructure and Electrical Properties of Thin Deposited on Metal Electrodes,xe2x80x9d Jpn. J. Appl. Phys., 37:1336-1338 (1998) report crystalline Ta2O5 layers having dielectric constants over 50 made by depositing the layers on platinum and ruthenium substrates rather than on poly-Si electrodes and annealing at 750xc2x0 C. For another example, Lin et al., xe2x80x9cTa2O5 thin films with exceptionally high dielectric constant,xe2x80x9d Applied Physics Newsletter, 74(16):2370-2372 (1999) report that if a Ta2O5 layer is deposited on a Ru/TiN/Ti/SiO2 layered substrate, its dielectric constant can be increased up to 90-110 after N2O plasma treatment and then rapid thermal nitridation (RTN) at 800xc2x0 C.
To date, efforts to improve the dielectric constant of Ta2O5 layers have either required high temperature processing that has led to various layer deficiencies or have required specialized processing or substrate considerations. Thus, there remains a need for a vapor deposition process to form Ta2O5 layers that have high dielectric constants and low current leakage, and that preferably do not require high temperature annealing, do not utilize oxidizers that can cause the formation of SiO2 interfacial layers on polysilicon substrates, and do not require specialized processing or substrate considerations.
The present invention is directed toward using a vapor deposition process using refractory metal precursor compounds and ethers to form refractory metal oxide layers, especially tantalum pentoxide (Ta2O5) layers, on substrates. The vapor deposition process is preferably a reactive vapor deposition process that involves co-reacting the precursor compounds and the ethers.
The methods of the present invention involve forming a refractory metal oxide layer on a substrate by using a vapor deposition process and one or more refractory metal precursor compounds of the formula MYn (Formula I), wherein M is a refractory metal, each Y is independently a halogen atom, and n is an integer selected to match the valence of the metal M, and one or more ethers of the formula R1xe2x80x94Oxe2x80x94R2, wherein R1 and R2 are each independently organic groups.
In one embodiment, a method of forming a layer on a substrate is provided that includes: providing a substrate (preferably a semiconductor substrate or substrate assembly such as a silicon wafer); providing a vapor that includes one or more refractory metal precursor compounds of the formula MYn, wherein M is a refractory metal (e.g., tantalum), each Y is independently a halogen atom (preferably, F, CI, I, or combinations thereof, and more preferably, F), and n is an integer selected to match the valence of the metal M (e.g., n=5 when M=Ta); providing a vapor that includes one or more ethers of the formula R1xe2x80x94Oxe2x80x94R2, wherein R1 and R2 are each independently organic groups (e.g., alkyl groups, alkenyl groups, aryl groups, silyl groups, and combinations thereof); and directing the vapors of the one or more refractory metal precursor compounds and the one or more ethers to the substrate to form a refractory metal oxide layer on one or more surfaces of the substrate.
The present invention also provides a method of manufacturing a memory device. The method includes: providing a substrate (preferably a semiconductor substrate or substrate assembly such as a silicon wafer) having a first electrode thereon; providing a vapor that includes one or more refractory metal precursor compounds of the formula MYn, wherein M is a refractory metal, each Y is independently a halogen atom, and n is an integer selected to match the valence of the metal M; providing a vapor that includes one or more ethers of the formula R1xe2x80x94Oxe2x80x94R2, wherein R1 and R2 are each independently organic groups; directing the vapors that include the one or more refractory metal precursor compounds and the one or more ethers to the substrate to form a refractory metal oxide dielectric layer on the first electrode of the substrate; and forming a second electrode on the dielectric layer.
The present invention also provides a vapor deposition apparatus that includes: a vapor deposition chamber having a substrate (e.g., a silicon wafer) positioned therein; and one or more vessels that include one or more refractory metal precursor compounds of the formula MYn, wherein M is a refractory metal, each Y is independently a halogen atom, and n is an integer selected to match the valence of the metal M; and one or more vessels that include one or more ethers of the formula R1xe2x80x94Oxe2x80x94R2, wherein R1 and R2 are each independently organic groups. Optionally, the apparatus includes one or more sources of an inert carrier gas for transferring the precursors to the vapor deposition chamber, and/or one or more vessels that include one or more metal-containing precursor compounds having a formula different from MYn.
The methods of the present invention can utilize a chemical vapor deposition (CVD) process, which can be pulsed, or an atomic layer deposition (ALD) process (a self-limiting vapor deposition process that includes a plurality of deposition cycles, typically with purging between the cycles). Preferably, the methods of the present invention use ALD. For certain ALD processes, the tantalum oxide layer is formed by alternately introducing one or more precursor compounds and ethers into a deposition chamber during each deposition cycle.
xe2x80x9cSubstratexe2x80x9d as used herein refers to any base material or construction upon which a metal-containing layer can be deposited. The term xe2x80x9csubstratexe2x80x9d is meant to include semiconductor substrates and also include non-semiconductor substrates such as films, molded articles, fibers, wires, glass, ceramics, machined metal parts, etc.
xe2x80x9cSemiconductor substratexe2x80x9d or xe2x80x9csubstrate assemblyxe2x80x9d as used herein refers to a semiconductor substrate such as a metal electrode, base semiconductor layer or a semiconductor substrate having one or more layers, structures, or regions formed thereon. A base semiconductor layer is typically the lowest layer of silicon material on a wafer or a silicon layer deposited on another material, such as silicon on sapphire. When reference is made to a substrate assembly, various process steps may have been previously used to form or define regions, junctions, various structures or features, and openings such as capacitor plates or barriers for capacitors.
xe2x80x9cLayerxe2x80x9d as used herein refers to any metal-containing layer that can be formed on a substrate from the precursor compounds of this invention using a vapor deposition process. The term xe2x80x9clayerxe2x80x9d is meant to include layers specific to the semiconductor industry, such as xe2x80x9cbarrier layer,xe2x80x9d xe2x80x9cdielectric layer,xe2x80x9d and xe2x80x9cconductive layer.xe2x80x9d (The term xe2x80x9clayerxe2x80x9d is synonymous with the term xe2x80x9cfilmxe2x80x9d frequently used in the semiconductor industry.) The term xe2x80x9clayerxe2x80x9d is also meant to include layers found in technology outside of semiconductor technology, such as coatings on glass.
xe2x80x9cDielectric layerxe2x80x9d as used herein is a term used in the semiconductor industry that refers to an insulating layer (sometimes referred to as a xe2x80x9cfilmxe2x80x9d) having a high dielectric constant that is typically positioned between two conductive electrodes to form a capacitor. For this invention, the dielectric layer is a refractory metal oxide layer, preferably a Ta2O5 layer, formed using a reactive deposition process.
xe2x80x9cRefractory metalxe2x80x9d as defined by Webster""s New Universal Unabridged Dictionary (1992) is a metal that is difficult to fuse, reduce, or work. For the purposes of this invention, the term xe2x80x9crefractory metalxe2x80x9d is meant to include the Group IVB metals (i.e., titanium (Ti), zirconium (Zr), hafnium (Hf)); the Group VB metals (i.e., vanadium (V), niobium (Nb), tantalum (Ta)); and the Group VIB metals (i.e., chromium (Cr), molybdenum (Mo) and tungsten (W)).
xe2x80x9cPrecursor compoundxe2x80x9d as used herein refers to refractory metal precursor compounds, tantalum precursor compounds, nitrogen precursor compounds, silicon precursor compounds, and other metal-containing precursor compounds, for example. A suitable precursor compound is one that is capable of forming, either alone or with other precursor compounds, a refractory metal-containing layer on a substrate using a vapor deposition process. The resulting metal-containing layers are typically oxide layers, which are useful as dielectric layers.
xe2x80x9cDeposition processxe2x80x9d and xe2x80x9cvapor deposition processxe2x80x9d as used herein refer to a process in which a metal-containing layer is formed on one or more surfaces of a substrate (e.g., a doped polysilicon wafer) from vaporized precursor compound(s). Specifically, one or more metal precursor compounds are vaporized and directed to one or more surfaces of a heated substrate (e.g., semiconductor substrate or substrate assembly) placed in a deposition chamber. These precursor compounds form (e.g., by reacting or decomposing) a non-volatile, thin, uniform, metal-containing layer on the surface(s) of the substrate. For the purposes of this invention, the term xe2x80x9cvapor deposition processxe2x80x9d is meant to include both chemical vapor deposition processes (including pulsed chemical vapor deposition processes) and atomic layer deposition processes.
xe2x80x9cChemical vapor depositionxe2x80x9d (CVD) as used herein refers to a vapor deposition process wherein the desired layer is deposited on the substrate from vaporized metal precursor compounds and any reaction gases used within a deposition chamber with no effort made to separate the reaction components. In contrast to a xe2x80x9csimplexe2x80x9d CVD process that involves the substantial simultaneous use of the precursor compounds and any reaction gases, xe2x80x9cpulsedxe2x80x9d CVD alternately pulses these materials into the deposition chamber, but does not rigorously avoid intermixing of the precursor and reaction gas streams, as is typically done in atomic layer deposition or ALD (discussed in greater detail below).
xe2x80x9cAtomic layer depositionxe2x80x9d (ALD) as used herein refers to a vapor deposition process in which numerous consecutive deposition cycles are conducted in a deposition chamber. Typically, during each cycle the metal precursor is chemisorbed to the substrate surface; excess precursor is purged out; a subsequent precursor and/or reaction gas is introduced to react with the chemisorbed layer; and excess reaction gas (if used) and by-products are removed. As compared to the one cycle chemical vapor deposition (CVD) process, the longer duration multi-cycle ALD process allows for improved control of layer thickness by self-limiting layer growth and minimizing detrimental gas phase reactions by separation of the reaction components. The term xe2x80x9catomic layer depositionxe2x80x9d as used herein is also meant to include the related terms xe2x80x9catomic layer epitaxyxe2x80x9d (ALE) (see U.S. Pat. No. 5,256,244 (Ackerman)), molecular beam epitaxy (MBE), gas source MBE, organometallic MBE, and chemical beam epitaxy when performed with alternating pulses of precursor compound(s), reaction gas and purge (i.e., inert carrier) gas.
xe2x80x9cChemisorptionxe2x80x9d as used herein refers to the chemical adsorption of vaporized reactive precursor compounds on the surface of a substrate. The adsorbed species are irreversibly bound to the substrate surface as a result of relatively strong binding forces characterized by high adsorption energies ( greater than 30 kcal/mol), comparable in strength to ordinary chemical bonds. The chemisorbed species are limited to the formation of a monolayer on the substrate surface. (See xe2x80x9cThe Condensed Chemical Dictionaryxe2x80x9d, 10th edition, revised by G. G. Hawley, published by Van Nostrand Reinhold Co., New York, 225 (1981)). The technique of ALD is based on the principle of the formation of a saturated monolayer of reactive precursor molecules by chemisorption. In ALD one or more appropriate reactive precursor compounds are alternately introduced (e.g., pulsed) into a deposition chamber and chemisorbed onto the surfaces of a substrate. Each sequential introduction of a reactive precursor compound is typically separated by an inert carrier gas purge. Each precursor compound co-reaction adds a new atomic layer to previously deposited layers to form a cumulative solid layer. The cycle is repeated, typically for several hundred times, to gradually form the desired layer thickness. It should be understood, however, that ALD can use one precursor compound and one reaction gas.